1. Field of the Invention
The present invention relates to an optical compensation film, an optical compensation film-integrated polarizing plate using the optical compensation film, and a liquid crystal display apparatus.
2. Description of the Related Art
Up to now, when a liquid crystal display apparatus is viewed in an oblique direction, there are a reduction in contrast and a change in hue and a viewing angle characteristic thereof is not sufficient as compared with a CRT display apparatus. Therefore, the improvement of the viewing angle characteristic is strongly desired. The viewing angle characteristic of the liquid crystal display apparatus is principally caused by the dependence on angle of birefringence of a liquid crystal cell. For example, a TN-mode liquid crystal display apparatus is excellent in display response speed and contrast and high in productivity, and thus widely used as a display unit of various apparatuses including OA devices such as a personal computer and a monitor. However, in a TN-mode liquid crystal cell, liquid crystal molecules are arranged in a tilt alignment with respect to upper and lower electrode substrates, and hence there is a problem that viewing angle dependence becomes larger, for example, a display image contrast changes depending on an observation angle to color an image area, to thereby reduce visibility. Therefore, it is strongly desired to compensate for the dependence on angle of birefringence (that is, retardation) of the liquid crystal cell using the optical compensation film, to improve the viewing angle characteristic.
One of methods of improving the viewing angle characteristic is to use a tilt alignment type optical compensation film in the TN-mode liquid crystal display apparatus. Examples of the tilt alignment type optical compensation film which have been reported include an optical compensation film containing low-molecular liquid crystal arranged in a tilt alignment in a polymer matrix (Japanese Patent No. 2565644) and an optical compensation film in which an alignment film is formed on a support and discotic liquid crystal is arranged in a tilt alignment on the alignment film to polymerize the discotic liquid crystal (Japanese Patent No. 2802719). However, the TN-mode optical compensation film as described above in which the liquid crystal material is arranged in a tilt alignment has the following problem (Japanese Patent Application Laid-open No. 2000-105315). For example, the selection of the liquid crystal material (for example, selection of liquid crystal material easily arranged in a tilt alignment based on surface energy difference in air interface) and the control of a tilt angle of the liquid crystal material (for example, control of tilt angle using surfactant) are required. An alignment substrate is essential, and hence a manufacturing method is complicated. The variety of control factors is wide, and hence it is difficult to adjust the tilt angle and retardation.
When the liquid crystal material is to be used, it is difficult to separately control liquid crystal molecules with high precision. Therefore, in view of a film, there is a problem that alignment fluctuations of the liquid crystal molecules occur and cause the cancellation of polarization to reduce the contrast of a liquid crystal panel.
Unlike a VA-mode or IPS-mode liquid crystal display apparatus, the TN-mode liquid crystal display apparatus includes a polarizing plate provided so that an absorption axis of a polarizer has an direction of 45° or 135° with respect to a lateral direction of the liquid crystal panel in view of characteristics. When a size of the polarizing plate changes in a high-temperature or a low-temperature environment and/or a high-humidity environment, a stress is applied to the optical compensation film because of the change in size, and hence distortion may occur. Therefore, light leakage occurs to cause brightness unevenness in a horizontal direction and vertical direction of the liquid crystal panel. This is a problem with respect to appearance uniformity.